An Ethernet network is typically defined on layer 2 in the Open Systems Interconnection model (OSI) provided by International Organization for Standardization (ISO). Layer 2 is also commonly referred to as the Data Link Layer in the OSI-model. An Ethernet network may typically comprise a large number of layer 2 switch or bridge devices, hereinafter referred to as bridge nodes. These bridge nodes may be interconnected and grouped in a large number of different ways in order to form different sub-networks or groups of bridge nodes. These groups of bridge nodes may commonly be referred to as layer 2 cloud networks or Ethernet networks, that is, networks of Layer 2 network devices (such as, switches or bridges) which are connected together via a ring or a meshed network. These groups of bridge nodes may also be connected to each other through a single common bridge node, which is commonly referred to as a root bridge node as illustrated in FIG. 1. The root bridge node may be a bridge node that is configured to act as a root bridge node. The root bridge node may be elected by a network protocol called Spanning Tree Protocol (STP) or be manually configured to act as the root bridge node.
STP is a network protocol that ensures a loop-free topology for an Ethernet network. STP may be employed to prevent loops in the groups of bridge nodes and the broadcast messaging resulting from such loops. STP is also standardized in the IEEE 802.1D standard. Hereinafter, xSTP is used to denote the different variations of STP that may be employed for the groups of bridge nodes, such as, for example, Rapid Spanning Tree Protocol (RSTP), Multiple Spanning Tree Protocol (MSTP) or any other variation of STP.
When implemented in a group of bridge nodes, xSTP creates a spanning tree within the meshed or ringed network of bridge nodes, and disables those links that are not part of the spanning tree, leaving a single active path between any two bridge nodes.
Ethernet switches residing in one of these layer-2 clouds can be variously connected to each other, letting to the RSTP protocol the task to remove any loop between them.
Although a number of layer-2 clouds (e.g. Ethernet networks) may be connected to the same root bridge node these layer-2 clouds have no relationship with each other. The root bridge node, in turn, does not know details of the number, the consistency and the connectivity of the layer-2 clouds connected to it. In known solutions information about layer-2 clouds (consistency, connectivity, etc) has to be manually entered in the root bridge node and it is assumed to be static. This means that the view of Ethernet network form the root bridge node must be statically configured by the operator, which, in turn, means that the operator has to associate each port of root bridge node to a specific layer-2 cloud, subjected to possible errors.